A number of laser levels already exist. A common form of such levelling apparatus uses a pendulum assembly inside an outer main body to carry the light emitting devices. One example of such an assembly is shown in FIGS. 1 and 2 of the drawings.
The inner pendulum assembly 100 provides a main body 101 mounted to rotate about its mounting axis defined by a blade edge 102 under the effect of gravity such that the assembly is residing in a substantially vertical plane. Light emitting devices 103 and 104 are provided and connected to the main body to emit light substantially transverse to the plane of the main body. Associated driving circuitry 107 is also connected to the main body.
Two adjustments are necessary in such an assembly. The first of these involves ensuring the light emitting devices, mounted on opposed sides of the main body, are substantially co-linear. To reduce costs, the main body itself may be cast or otherwise formed without high tolerances. Once the light emitting devices 103 and 104 are fitted substantially opposite each other, each needs to be adjusted to ensure the beam of light emitted is substantially parallel with the other. Hence adjustment mechanisms 105 and 106 are provided to bear on the casing of the light emitting devices and push the casing into alignment with the opposed device.
The second form of adjustment is to ensure the co-linear beams from the level emit substantially horizontally. It will be appreciated that the co-linear beams may be at a slight angle to the horizontal if the gravity aligned main body rests in a position pulling one beam up and the other down from their intended positions. These may be brought into alignment by adjusting the centre of gravity of the pendulum assembly 100 through the rotation of adjusting weights 108 and 109 to draw these towards or away from a axis of rotation of the main body.
Such adjustments all introduce extra work in fitting the light emitting devices and producing a pendulum assembly that is suitable for work conditions. Furthermore, each additional adjustment mechanism provides the possibility of the level losing adjustment over time and requiring recalibration.